Effects of nicotinic acid on respiratory exchange ratio and substrate levels during exercise.

The purpose of this study was to investigate the effects of pharmacologic treatment with nicotinic acid (NA) (3 g NA.d-1) on fuel utilization during exercise and on total and HDL-cholesterol levels of trained runners. Eight experienced male runners performed four 30-min submaximal treadmill runs (SUB) at approximately 60% of aerobic capacity: the first served as the control condition, whereas SUBs 2, 3, and 4 were conducted at the onset, midpoint, and conclusion of the 3-wk NA treatment period. A 1-g NA dose was ingested 1 h prior to SUBs 2-4, which were conducted in the morning following a 12-h fast. The respiratory exchange ratio (RER) was significantly higher during SUBs 2, 3, and 4 (0.919 +/- 0.009, 0.898 +/- 0.007, and 0.896 +/- 0.009, respectively) than during SUB1 (0.871 +/- 0.008); and the RER during SUB2 was also significantly higher than that during SUB3 and SUB4 (P < 0.001). Serum free fatty acid (FFA) and glycerol levels were significantly lower during SUBs 2, 3, and 4 as compared with SUB1 (P < 0.001). Total cholesterol showed a significant decrease (from 195.3 +/- 9.2 to 174.5 +/- 9.2 mg.dl-1) and HDL cholesterol showed a significant elevation (from 56.2 +/- 2.9 to 63.0 +/- 3.9 mg.dl-1) during the NA treatment period (P < 0.05). The RER, FFA, and glycerol data demonstrate a persistent inhibition of fat utilization during submaximal exercise due to NA treatment. The 3-wk NA treatment period also proved to be sufficient to effect changes in total and HDL-cholesterol levels of these runners.